IEEE 802.11 is a set of media access control (MAC) and physical layer (PHY) specification for implementing wireless local area network (WLAN) computer communication in the Wi-Fi (2.4, 3.6, 5, and 60 GHz) frequency bands. The standards and amendments provide the basis for wireless network products using the Wi-Fi frequency bands. For example, IEEE 802.11ac is a wireless networking standard in the 802.11 family providing high-throughput WLANs on the 5 GHz band. Significant wider channel bandwidths (20 MHz, 40 MHz, 80 MHz, and 160 MHz) were proposed in the IEEE 802.11ac standard. The High Efficiency WLAN study group (HEW SG) is a study group within IEEE 802.11 working group that considered the improvement of spectrum efficiency to enhance the system throughput in high-density scenarios of wireless devices. At the conclusions of HEW SG, TGax was formed and tasked to work on IEEE 802.11ax standard that will become a successor to IEEE 802.11ac.
In IEEE 802.11ac, a transmitter of a BSS (basis service set) of certain bandwidth is allowed to transmit radio signals onto the shared wireless medium depending on clear channel assessment (CCA) sensing and a backoff or deferral procedure for channel access contention. For a BSS of certain bandwidth, a valid transmission sub-channel shall have bandwidth, allowable in the IEEE 802.11ac, equal to or smaller than the full bandwidth of the BSS and contains the designated primary sub-channel of the BSS. Based on the CCA sensing in the valid transmission bandwidths, the transmitter is allowed to transmit in any of the valid transmission sub-channels as long as the CCA indicates the sub-channel is idle. This dynamic transmission bandwidth scheme allows system bandwidth resource to be efficiently utilized.
An enhanced distributed channel access protocol (EDCA) is used in IEEE 802.11ac as a channel contention procedure for wireless devices to gain access to the shared wireless medium, e.g., to obtain a transmitting opportunity (TXOP) for transmitting radio signals onto the shared wireless medium. The simple CSMA/CA with random back-off contention scheme and low cost ad hoc deployment in unlicensed spectrum have contributed rapid adoption of Wi-Fi systems. Typically, the EDCA TXOP is based on activity of the primary channel(s), while the transmit channel width determination is based on the secondary channel CCA during an interval (PIFS) immediately preceding the start of the TXOP. The basic assumption of EDCA is that a packet collision can occur if a device transmits signal under the channel busy condition when the received signal level is higher than CCA level.
Based on the baseline EDCA medium access rules, AP and non-AP STAs have roughly equal probability of gaining medium contention. In IEEE 802.11ax, AP has higher frequency of accessing the medium. In addition to AP accessing the medium for SU and MU downlink traffic, AP also transmits trigger frames to start the uplink MU traffic, which includes aggregation of uplink resource units from multiple non-AP station in frequency domain (e.g., OFDMA) or uplink spatial streams from multiple non-AP stations. In a dense environment, medium access become difficult due to increased medium traffic and larger number of contending nodes, leading to AP starvation issue. This can significantly penalize 802.11ax network, affecting both downlink and uplink traffic.
If 802.11ax APs employ prioritized EDCA parameters to increase their probability of gaining medium contention, it raises the issues of fairness to the co-existing legacy APs/STAs that operate without prioritized EDCA parameters. As a result, it aggregates the AP starvation issue in the legacy networks when co-exist with 802.11ax networks. Another issue is secondary channel underutilization during uplink access, when STA transmits in narrow channel, or when STA detects secondary channel busy (but AP does not detect secondary channel busy).
A solution is sought.